California INDOOR AIR QUALITY Program RADON & INDOOR AIR

Radon in California: Current State of Knowledge

New: The California Sierra Radon Study Final Report, March 2005

STATEWIDE RADON SURVEYS OF CALIFORNIA HOMES & SCHOOLS
Statewide study of residential radon concentrations was carried out by the California Department of Health Services (CDHS) in 1988-89.  The survey was a statewide effort to determine the extent of indoor radon exposure in representative California homes and to identify areas of the State where residences may have elevated radon concentrations.  In this study, radon monitors were placed in 310 residences.  Measurements were carried out for a full year to obtain an accurate estimate of exposure unbiased by short-term fluctuations in radon levels because of weather conditions or changes in ventilation.  The survey determined the proportion of homes exceeding the action level of 4 picocuries per liter (pCi/L) of air recommended by the U. S. EPA.  Homes with long-term concentrations measured at or above the action level are recommended for radon reduction.  The U.S. EPA action level is largely based on current mitigation technologies. It is recognized that radon exposures below 4 pCi/L still contribute to the risk of lung cancer.

The statewide survey showed that about 0.8% (approximately 100,000) of California homes are expected to have annual average radon levels exceeding the U.S. EPA action level.  These results confirmed the magnitude of high radon homes found in earlier limited studies and another statewide radon survey by CDHS and U.S.EPA using short-term monitors.  The geometric mean (GM) for long-term radon concentrations in the state was 0.85 pCi/L.

Related DHS Publications

Survey of Residential Indoor and Outdoor Radon Concentrations in California,
Liu K-S, Hayward SB, Girman JR, et al., 1990.
Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.

Annual Average Radon Concentrations in California Residences,
Liu KS, Hayward SB, Girman JR, Moed BA and Huang FY, 1991,
J. Air and Waste Mgmt. Assoc. 41:1207-1212.

The Distribution of Lifetime Cumulative Exposures to Radon for California Residents,
Liu KS, Chang YL, Hayward SB, Gadgil AJ and Nero AJ, 1993
Journal of Exposure Analysis and Environmental Epidemiology. 3:165-179.

Survey of Indoor Radon Concentrations in California Elementary Schools Executive Summary Full Report

Zhou J, Liu KS, and Waldman J, May 1998
Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.

Environmental Health Laboratory Branch Report CA/DHS/EHLB/R-140.

SURVEYS IN SELECTED REGIONS OF CALIFORNIA
The results also were analyzed by dividing the state into six geographic regions.  The highest level was measured in the Sierra Nevada region (from Placer south to Mariposa, as well as Alpine, Mono, Inyo counties), which was significantly higher than other areas (GM=2.2 pCi/L).  The limited data for this region in the statewide survey indicated 11-45% of homes are above the U.S. EPA action level.  The Fresno-Ventura region (Madera, Fresno, Kings, Tulare, Kern, Santa Barbara, Ventura counties) had the next highest level (GM=1.3 pCi/L).

In 1991, a focused survey of residential radon levels was carried out in 862 residences of Ventura and northwestern Los Angeles.  It determined 1-14% of homes in this region had long-term radon exposure above the U.S. EPA action level.  More recently, DHS finalized a survey of residential radon levels in homes and schools in the Sierra Foothill region. This study provides population-averaged long-term radon exposure from representative samples of residences and elementary schools in the California Sierra Region. In residences, the average annual radon exposure is 1.3 pCi/l, with about 3% of residences in the region exceeding the 4 pCi/l. The average school-year exposure in the elementary school classrooms is 1.1 pCi/l, with 2% of the classrooms exceeding 4 pCi/l.

Related Publications

Survey of Residential Radon Levels in Ventura County and Northwestern Los Angeles County,
Liu K-S, Chang Y-L, Hayward SB, 1991.
Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.

The California Sierra Radon Study Final Report Executive Summary Full Report

Tsai F and Waldman JM, March 2005

Report by CA Department of Health Services, Indoor Air Quality Section, Berkeley, CA.

Environmental Health Laboratory Branch Report CA/DHS/EHLB/R-173.

IMPLICATIONS OF THE RADON SURVEYS
Overall, the accumulating data continue to show that California does not have a substantial statewide problem with indoor radon exposure.  However, elevated radon levels are found in certain selected areas.  Nonetheless, the magnitude of the radon concentrations for residences and schools in these regions are relatively moderate, as compared to other high radon risk regions in the U.S. Because both residential radon concentrations and smoking prevalence are relatively low in California, effective radon risk management options are limited. Nonetheless, health risks associated with residential radon are substantial, and results of this study could be used as the basis to develop intervention policies, such as outreach to smoking households in identified hot spots for radon screening and follow-up smoking-cessation programs.

Useful Links

General Information
Indoor Air Quality - U.S. EPA Radon Publications
EPA Map of Radon Zones for California Counties

Health Effects
Health Effects of Exposure to Indoor Radon: BEIR VI report
RADON: A Physician's Guide - The Health Threat with a Simple Solution

Measurements
List of Radon Service Providers & Free Radon Kit from California DHS Radon Program

National Radon Proficiency Program

National Radon Safety Board

Radon Reduction
Consumer's Guide to Radon Reduction
Radon Mitigation Standards
Model Standards and Techniques for Control of Radon in New Residential Buildings

Radon in Drinking Water

Proposed Radon in Drinking Water Rule

Office of Ground Water and Drinking Water
NAS Report on Radon in Drinking Water

How to contact us: Call: IAQ Assistance Line:  510-620-2874

Mail: DHS - IAQ Program

850 Marina Bay Parkway

(M.S. G365 / EHLB)

Richmond, CA 94804

E-mail: IAQ Staff

Fax: 510-620-2825